Nutritional factors can have profound influence on immune defense, but the mechanisms linking dietary nutrition to immunity are poorly understood. Work performed under the proposed project will establish the relationship between nutrition and defense from physiological and genetic perspectives, and will ultimately identify genes contributing to individual-specific alteration in immunity due to diet. The project will make use of the model insect Drosophila melanogaster, which has metabolic and immune systems that are highly conserved with homologous systems in vertebrates. In Aim 1 of the project, D. melanogaster provided with diets of varying nutritional composition will be evaluated for resistance to bacterial infection (measured as immune system activity and suppression of bacterial proliferation) and tolerance of infection (measured as the ability to sustain health while infected). The experimental diets to be evaluated will vary in protein, sugar and fat levels. Aim 2 of the project will test the hypothesis that specific immune and metabolic signaling pathways are linked during infection, such that activation of the immune system causes altered metabolism and energetic utilization. The IMD (immune system), JNK (stress response), and insulin-like (metabolism) signaling pathways will be genetically disrupted to test for cross-communication between processes during the early stages of an infection. Aim 3 of the project will conceptually link the first two Aims in a study of naturally occurring variation. It is known that individuals in natural populations are genetically variable for both immune-related and metabolic traits. Experiments to be performed under Aim 3 will determine the degree to which resistance and tolerance phenotypes are determined by genotype-specific effects of diet (termed genotype-by-environment interaction). These interactions form the conceptual basis of personalized medicine, and understanding them will be crucial for advanced clinical therapeutics. Analysis of known polymorphisms and unbiased genome-wide association mapping will be employed to identify genes responsible for genotype-specific immunological alteration with diet. The data collected under all three Aims will provide novel and broadly comprehensive understanding of dietary effects on defense quality, with critical implications for clinical and evolutionary biology.